Occasionally, when a board covered with a brittle surface such as melamine, plastic-laminated, or other type of veneer needs to be sawn; the brittle material tends to break in an uncontrolled manner, especially at the edges of the board.
Two types of circular saw blades are usually used in order to avoid breaking of the edges: a leading saw blade followed by a main saw blade. The leading saw blade is used to produce a slit in the edge of the board, the slit is slightly broader than the cut made by the main saw. The presence of the broader slit at the edge prevents the main saw blade form violently breaking the edge.
The leading saw usually comprises two blades adjacently arranged, and coupled by a locking bolt. The profile, and in other words the width of the slit corresponds to the main saw, being slightly broader than the profile of the main saw, leaving small room on either sides of the main saw, so as to allow the main saw to cut through the board within the boundaries of the slit, thus preventing violent chopping of the board's edge.
A common way of achieving this is to provide a combined leading saw comprised of the two saw blades coupled together while keeping a slight distance between them, in a manner which leaves the sawing teeth of the discs partially overlapping. By varying the distance between the discs the width of the combined saw can be adjusted according to the needs of the user. In most cases, the profile of the combined saw is determined by trial and error.
There are a few ways for changing the width of the leading saw. One of the simplest and popular solutions is to provide corresponding shims having different widths; the shims are positioned between the adjacent discs. This solution is highly time-consuming since the blades have to be separated each time the width needs to be changed, and in a trial and error process, it hinders the work.
Other solutions were introduces by Leitz and GUHDO® from Germany. In one of the solutions, a separator is installed between the blades and its width is adjustable to allow variations in the distance between the blades. The separator consists of numerous parts and is complicated, and therefore rather difficult to operate. Moreover, the separator is designed to work with certain types of circular saw blades machines but not with others and is therefore not universally applicable.